Epsilon Archive for Student Projects

Abstract

Beet curly top virus (BCTV) is one of the most devastating DNA viruses, causing curly top diseases in a wide range of plants. This virus belongs to the family Geminiviridae, which replicate their circular single-stranded DNA genomes in the plant cell’s nucleus through employing host replication factors. Transcription and replication are mediated by double-stranded DNA that associates with cellular histone proteins to form minichromosomes. Plants apply different defence mechanisms against geminiviruses. Among them, viral genome methylation is considered as an epigenetic defence, which targets the viral DNA cytosine residues and histone H3 at lysine 9 (H3K9), using a small RNA-directed methylation pathway. On the other hand, TERMINAL FLOWER 2 (TFL2) is a protein in Arabidopsis that is essential in the transition from vegetative to reproductive phase. This protein is associated with silencing of multiple euchromatin genes related to plant development, such as flowering and floral organ identity, through recognition of trimethylated H3 at lysine 27 (H3K27). This study was planned to investigate whether TFL2 plays a role in chromatin methylation of BCTV. Thus, in infection experiments, the terminal flower 2 (tfl2) mutants of Arabidopsis were inoculated with BCTV to test if they show hypersusceptibility to the virus. However, no severe symptom was detected in these mutant plants in response to BCTV, suggesting that TFL2 does not play an important role in the defence against BCTV. To test the hypothesis that TFL2 binds to the geminiviral chromatin in vivo, TFL2-GFP transgenic Arabidopsis plants inoculated with BCTV, were tested in a chromatin immunoprecipitation (ChIP) assay. The method was planned based on immunoprecipitation of TFL2-GFP bound to the viral chromatin, using specific antibodies against GFP. The precipitated DNA obtained from the ChIP assay showed some amplification of the viral coat protein gene suggesting the possibility of an interaction between the TFL2 protein and BCTV chromatin.